CN109152118A - Tundish electromagnetic induction heating system multi layer control method - Google Patents

Tundish electromagnetic induction heating system multi layer control method Download PDF

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CN109152118A
CN109152118A CN201710664749.XA CN201710664749A CN109152118A CN 109152118 A CN109152118 A CN 109152118A CN 201710664749 A CN201710664749 A CN 201710664749A CN 109152118 A CN109152118 A CN 109152118A
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bridge arm
instruction
voltage
current
control
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CN109152118B (en
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罗安
何志兴
易伟浪
陈燕东
徐千鸣
岳雨霏
郭鹏
黄旭程
洪乐荣
王�锋
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Hunan University
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Hunan University
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/06—Control, e.g. of temperature, of power
    • H05B6/08—Control, e.g. of temperature, of power using compensating or balancing arrangements
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
    • H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
    • H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M5/275—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/293—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
    • H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
    • H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M5/275—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/293—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M5/2932—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage, current or power
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2206/00—Aspects relating to heating by electric, magnetic, or electromagnetic fields covered by group H05B6/00
    • H05B2206/02—Induction heating

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • General Induction Heating (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a kind of tundish electromagnetic induction heating system multi layer control method, temperature of top control is accurately adjusted for tundish weld temperature, and voltage balancing control then maintains the capacitance voltage of induction heating power to stablize；Middle layer predictive current control then realizes the AC input current, loop current and the collaboration optimization tracking for exporting electric current of induction heating power；Bottom includes switch motion distribution and Pressure and Control, and switch motion is distributed to the power modules of induction heating power and submodule capacitor voltage is maintained to balance.Temperature of top control acquires output current-order, input current instruction and loop current with voltage balancing control and instructs.The present invention is realized to tundish electromagnetic induction heating system temperature, input current, the multi objective control for exporting electric current, module voltage.

Description

Tundish electromagnetic induction heating system multi layer control method
Technical field
The present invention relates to a kind of tundish electromagnetic induction heating system multilayer controls for handing over alternation to change based on modular multilevel Method processed is suitable for the occasion of the high-power tundish electromagnetic heating of medium-frequency high-voltage.
Background technique
With the progress of power electronics and semiconductor technology, high-power high-efficiency variable-frequency power sources is greatly promoted Steel are heat-treated the development of induction heating technique, and tundish induction system is as the transformation series for converting electrical energy into molten steel thermal energy System induces electromotive force by the electric current of output alternation in molten steel, and then generates induced current.Induced current is in molten steel Flowing generates heating of the Joule heat completion to molten steel, completes the transformation of electric energy to thermal energy.Tundish electromagnetic induction heating system is logical Reduction molten steel overheat is crossed, and maintains constant temperature casting, and then promotes rolling shapes, is the core dress for producing the pure steel of high-quality It is standby.Tundish electromagnetic induction heating system has power big, and output voltage grade is high, and current control accuracy requires the features such as high. Therefore, there is good theoretical and engineering significance to the research of tundish induction heating system control method.
Recently as the development of Metallurgy Industry, the mid-frequency induction heating load of extensive smelting enterprise is also more and more.Mesh The power supply of preceding induction heating intermediate frequency furnace load mostly uses greatly AC-DC-AC three-level variation.Multiwinding transformer is whole with diode Stream obtains uncontrollable direct current, and the input voltage as rear class H bridge module, and the multiple H bridge output cascades of rear class realize high pressure Exchange output；Simple, the reliable advantage of structure with control, but winding structure is complicated, it is bulky.
In recent years, the tundish induction heating power based on the more level blocks of H bridge sub-module cascade has structural module, The advantages of output characteristics is ideal, more redundancies has obtained extensive concern and research.Based on the cascade more level blocks of H bridge module Change converter (MMC) structure, the transformation of AC-AC can be directly realized by, and have many advantages, such as to and fro flow of power, is tundish electricity The developing direction of magnetic induction heating system.Based on the tundish electromagnetic induction heating system that modular multilevel hands over alternation to change, protect Multiple control targets are protected, and control accuracy requirement is high, control strategy is the emphasis of research.
Summary of the invention
The present invention is intended to provide a kind of tundish electromagnetic induction heating system multi layer control method, is realized to tundish electromagnetism Induction heating system temperature, input current, the multi objective control for exporting electric current, module voltage.
In order to solve the above technical problems, the technical scheme adopted by the invention is that: a kind of tundish electromagnetic induction heating system System multi layer control method, including top layer control section, middle layer control section and bottom control part；The top layer control section Including balancing control section and alternate balance control section between whole machine balancing control section, bridge arm；
The whole machine balancing control section includes: all submodule capacitor electricity of acquisition six bridge arms of electromagnetic induction heating system Press udxi, and sum and obtain the total capacitance voltage of six bridge armsThe total capacitance voltage addition of six bridge arms is averaged again To global voltage average value udav, global voltage average value udavWith instruction valueIt controls to obtain three-phase alternating current input through PI after making difference The d axis control instruction of electric currentThe q axis control instruction of three-phase alternating current input currentIt is set as zero, d axis and q axis control instruction It converts to obtain three-phase alternating current instruction through dq/abcMaintain all submodule balances of voltage of electromagnetic induction heating system；Its In, x=a, b, c；
It includes: that each phase upper and lower bridge arm total capacitance voltage is obtained three-phase bridge arm electricity as difference that control section is balanced between the bridge arm Pressure differential deltap uda,ΔudbWith Δ udc, Δ udbWith Δ udcThe sum of again with 2* Δ udaIt is poor to make, and the instruction of negative phase-sequence circulation is obtained after PI is controlled D axis control instruction；ΔudcWith Δ udbIt is poor to make, and the q axis control instruction of negative phase-sequence circulation instruction, d axis and q are obtained after PI is controlled Axis control instruction converts to obtain the instruction of three-phase negative/positive loop current through dq/abcWithMaintain three-phase upper and lower bridge arm Capacitor voltage balance；
The alternate balance control section includes: that each phase upper and lower bridge arm total capacitance voltage is summed respectively, obtains three-phase bridge Arm voltage and ∑ udai,∑udbiWith ∑ udci, ∑ udbWith ∑ udcThe sum of with 2* ∑ udaIt is poor to make, and positive sequence circulation is obtained after PI is controlled The d axis control instruction of instruction；∑udbWith ∑ udcIt is poor to make, and the q axis control instruction of positive sequence circulation instruction, d axis are obtained after PI is controlled It converts to obtain the instruction of three-phase positive sequence loop current through dq/abc with q axis control instructionWithMaintain the electricity of three-phase bridge arm Hold the balance of voltage；
The middle layer control section includes: to establish following objective optimization function: Wherein c1And c2Respectively indicate differential mode voltage and common-mode voltage Control the weight factor of target；For differential mode voltage reference value, instructed by circulationIt is calculated according to prediction algorithm,For common-mode voltage reference value, instructed by exchange inputIt is calculated according to prediction algorithm；usxIt (k+1) is differential mode electricity Pressure；ucxIt (k+1) is common-mode voltage；It selects to make the optimal output level of the smallest level combinations of objective optimization functional value, obtain The optimization output level number n of bridge arm and lower bridge arm next control periodux(k+1) and nlx(k+1)；
The bottom control part includes: the upper bridge arm obtained according to middle layer predictive current control and the next control of lower bridge arm The optimization output level number in period processed, switch motion is distributed to the submodule of each bridge arm and submodule capacitor voltage is maintained to put down Weighing apparatus.
The d axis control instruction of three-phase alternating current input currentWherein kpFor PI control Scale parameter processed, kiRespectively PI controls time of integration parameter.
Three-phase alternating current instructs expression formula are as follows:
ωgFor synchronized angular frequency.
The instruction of three-phase negative/positive loop currentWithExpression formula are as follows:Wherein,
ωgFor synchronized angular frequency.
The instruction of three-phase positive sequence loop currentWithExpression formula are as follows:
Wherein,
θ=ω0T, ω0Angular frequency is given for induced current.
The specific implementation process of the bottom control part includes:
Each bridge arm submodule capacitor voltage is acquired, and bridge arm submodule capacitor voltage is ranked up as ascending；
As upper bridge arm current iuxMore than or equal to 0, optimization exports upper bridge arm level number nux(k+1) it when being more than or equal to 0, presses Phototypesetting sequence is as a result, select the upper the smallest n of bridge arm Neutron module capacitance voltage valueux(k+1) a submodule exports 1 level, other sons Module exports 0 level；Work as iuxMore than or equal to 0, and optimize output level number nux(k+1) less than 0 when, according to ranking results, choosing Select the maximum n of bridge arm Neutron module capacitance voltage valueux(k+1) a submodule output -1, other submodules export 0 level；
Instantly bridge arm current ilxMore than or equal to 0, optimization output lower bridge arm level number nlx(k+1) it when being more than or equal to 0, presses Phototypesetting sequence is as a result, the selection the smallest n of lower bridge arm Neutron module capacitance voltage valuelx(k+1) a submodule exports 1 level, other sons Module exports 0 level；Work as ilxMore than or equal to 0, and optimize output level number nlx(k+1) less than 0 when, according to ranking results, choosing Select the maximum n of lower bridge arm Neutron module capacitance voltage valuelx(k+1) a submodule output -1, other submodules export 0 level；
As upper bridge arm current iuxLess than 0, optimization exports upper bridge arm level number nux(k+1) when being more than or equal to 0, according to sequence As a result, selecting the upper maximum n of bridge arm Neutron module capacitance voltage valueux(k+1) a submodule output 1,0 electricity of other submodules output It is flat；Work as iuxLess than 0, and optimize output level number nux(k+1) less than 0 when, according to ranking results, bridge arm Neutron module in selection The smallest n of capacitance voltage valueux(k+1) a submodule output -1, other submodules export 0 level；
Instantly bridge arm current ilxLess than 0, optimization output lower bridge arm level number nlx(k+1) when being more than or equal to 0, according to sequence As a result, the selection maximum n of lower bridge arm Neutron module capacitance voltage valuelx(k+1) a submodule output 1,0 electricity of other submodules output It is flat；Work as ilxLess than 0, and optimize output level number nlx(k+1) less than 0 when, according to ranking results, lower bridge arm Neutron module is selected The smallest n of capacitance voltage valuelx(k+1) a submodule output -1, other submodules export 0 level；
When submodule output 1, left side bridge arm upper tube is open-minded, and down tube is closed, and the right bridge arm upper tube is closed, and down tube is open-minded； When submodule output -1, left side bridge arm upper tube is closed, and down tube is open-minded, and the right bridge arm upper tube is open-minded, and down tube is closed；Work as submodule When exporting 0, left side bridge arm upper tube is closed, and down tube is open-minded, and the right bridge arm upper tube is closed, and down tube is open-minded or left side bridge arm upper tube Open-minded, down tube is closed, and the right bridge arm upper tube is open-minded, and down tube is closed.
Using multi layer control method, top layer is that temperature controls and voltage balancing control, middle layer are predictive current control, bottom Including switch motion distribution and Pressure and Control.Temperature of top control acquires output current-order, input electricity with voltage balancing control Stream instruction and loop current instruction are used as middle layer predictive current control target, and middle layer predictive current control acquires optimal output level Input of the number as bottom control.Switch motion is distributed to submodule and is maintained by bottom switch motion distribution and Pressure and Control The balance of submodule capacitor voltage.
Compared with prior art, the advantageous effect of present invention is that: use multi layer control system, can be realized and be The multiple target cooperatives control for temperature, input current, output electric current, the module voltage of uniting, while electric current is predicted using Optimized model Control, can reduce the calculation amount of numerical control system, and realize AC input current, loop current and the collaboration for exporting electric current Optimal control, and there is quick dynamic response characteristic.
Detailed description of the invention
Fig. 1 is the tundish electromagnetic heating system topology diagram that modular multilevel hands over alternation to change；
Fig. 2 is three layers of control block diagram；
Fig. 3 (a)~Fig. 3 (d) is temperature of top and voltage balancing control block diagram；
Fig. 4 is the predictive current control block diagram based on limited control set；
Fig. 5 is submodule capacitor voltage balance flow chart.
Specific embodiment
Fig. 1 show the tundish electromagnetic heating system topological structure for handing over alternation to change for modular multilevel of the invention Figure, input terminal is three-phase alternating-current supply, uga, ugb,ugcRespectively A, B, C three-phase alternating current phase voltage, isa, isb, iscRespectively three Phase input current, output end are midfrequent AC, are connected with tundish electromagnetic heater, uoFor output voltage.How electric modularization is Usual friendship AC-AC converter is made of three-phase bridge arm, and every phase bridge arm uses N number of H bridge sub-module cascade, and each bridge arm passes through two bridge arms Inductance L is connected.iux, ilx(x=a, b, c) respectively indicates the electric current that each phase upper and lower bridge arm flows through, uux, ulx(x=a, b, c) difference Indicate each phase upper and lower bridge arm equivalent voltage value.
Fig. 2 show the AC input current circuit of tundish electromagnetic heating system that modular multilevel hands over alternation to change and Circulation equivalent-circuit model.In conjunction with KVL, KCL establishing equation differential mode voltage and common-mode voltage equivalent model are as follows:
Wherein:
Wherein usx, ucx(x=a, b, c) is respectively each phase differential mode voltage and common-mode voltage, isx, icx(x=a, b, c) is defeated Enter electric current and circulation.
Fig. 2 show three layers of control strategy, and top layer is temperature and voltage balancing control, and middle layer is predictive current control, bottom Layer is switch motion distribution and Pressure and Control.Temperature of top and voltage balancing control include temperature control, balance control between bridge arm, The control of alternate balance, whole machine balancing control, control to obtain instruction value by temperature beThe negative phase-sequence obtained by balancing control between bridge arm Circulation instructsIt is by the current instruction value that alternate balance control obtainsThree passes through (11) formula Obtaining circulation instruction value isThe instruction value of the AC input current controlled by whole machine balancing isIt is finally circulation instruction by the instruction that temperature of top and the balance of voltage obtainAnd AC input current InstructionMiddle layer uses the Model Predictive Control based on limited control set, is calculated according to current control instruction defeated The predicted value of voltage out, according to upper and lower bridge arm output voltage combine, calculate each level combinations for output voltage.Root again According to objective optimization function, the majorized function value that each level combinations define is calculated, and is compared, selection makes objective optimization function It is worth output level instruction of the smallest output level combination as each bridge arm in next control period.Bottom is switch motion point Match and Pressure and Control, the optimization in the upper bridge arm and lower bridge arm obtained according to middle layer predictive current control next control period export Level number nux(k+1) and nlx(k+1) switch motion is distributed to the submodule of each bridge arm and maintains submodule by (x=a, b, c) Block capacitor voltage balance.The temperature T, submodule voltage u that finally will testdxi, circulation icx, AC input current isx, defeated Voltage u outoEtc. parameters feed back to after processing top layer control and middle layer control.Wherein the processing of parameter is as follows:
Δudx=∑ ulxi-∑uuxi (5)
Δudx(x=a, b, c) is three-phase bridge arm voltage difference, ∑ udx(x=a, b, c) three-phase bridge arm voltage and,It is six The total capacitance voltage of bridge arm.
Fig. 3 (a)~Fig. 3 (d) is temperature of top and voltage balancing control block diagram.Fig. 3 (a) is temperature control, temperature control Using PID controller, the temperature that will test and given temperature instruction value are made the difference, difference after PID control again with output electric current Synchronization signal be multiplied, obtain zero-sequence current instruction valueFig. 3 (b) is whole control balance, and whole machine balancing is for maintaining induction All submodule balances of voltage of heating power supply, by the total capacitance voltage of six bridge armsIt is made the difference with total voltage reference value Error signal, with synchronized signal multiplication, obtains AC input current signal after PI controllerFig. 3 (c) is between bridge arm Balance control, each phase upper and lower bridge arm total capacitance voltage obtain three-phase bridge arm voltage difference delta u as differenceda,ΔudbWith Δ udc。ΔudbWith ΔudcThe sum of again with 2* Δ udaIt is poor to make, and the d axis control instruction of negative phase-sequence circulation instruction is obtained after PI is controlled；ΔudcWith Δ udbMake Difference obtains the q axis control instruction of negative phase-sequence circulation instruction after PI is controlled, and d axis and q axis control instruction convert to obtain three through dq/abc The instruction of phase negative phase-sequence loop currentFig. 3 (d) is alternate balance control, each phase upper and lower bridge arm total capacitance voltage difference Summation obtains three-phase bridge arm voltage and ∑ uda,∑udbWith ∑ udc。∑udbWith ∑ udcThe sum of again with 2* ∑ udaIt is poor to make, and controls through PI The d axis control instruction of positive sequence circulation instruction is obtained afterwards；∑udbWith ∑ udcIt is poor to make, and the q of positive sequence circulation instruction is obtained after PI is controlled Axis control instruction, d axis and q axis control instruction convert to obtain the instruction of three-phase positive sequence loop current through dq/abc
Fig. 4 is the predictive current control block diagram based on limited control set, with each phase upper and lower bridge arm output level group cooperation For limited control set.The circulation instruction obtained with each phase top layerIt is instructed with input is exchanged As Kth+1 time Collaborative Control target ,+1 differential mode voltage instruction value of kth obtained according to prediction algorithmWith common mode electricity Press instruction valueAnd objective optimization function g is established, using the combination of upper and lower bridge arm output level as limited control set, The corresponding objective optimization functional value of each level combinations of cycle calculations, and recycle and compare, final choice makes objective optimization functional value The smallest level combinations are optimal output level, obtain the optimization output level number n of bridge arm and lower bridge arm next control periodux (k+1) and nlx(k+1)。
Fig. 5 is that submodule capacitor voltage balances flow chart.It is assumed that left side bridge arm upper tube is open-minded when submodule output 1, under Pipe is closed, and the right bridge arm upper tube is closed, and down tube is open-minded；When submodule output -1, left side bridge arm upper tube is closed, and down tube is open-minded, The right bridge arm upper tube is open-minded, and down tube is closed；When submodule output 0, left side bridge arm upper tube is closed, and down tube is open-minded, the right bridge arm Upper tube is closed, and down tube is open-minded or left side bridge arm upper tube is open-minded, and down tube is closed, and the right bridge arm upper tube is open-minded, and down tube is closed.Then Flow chart implementation procedure is as follows:
1) each bridge arm submodule voltage is acquired, and bridge arm submodule capacitor voltage is ranked up as ascending.
2) as bridge arm current iux(upper bridge arm) is greater than or equal to 0, and optimizes output level number nux(k+1) (upper bridge arm) is big When being equal to 0；By ranking results, submodule capacitor voltage is selected to be worth the smallest nux(k+1) (upper bridge arm) a submodule output 1, Other submodules output 0.
3) as bridge arm current iux(upper bridge arm) is greater than or equal to 0, and optimizes output level number nux(k+1) (upper bridge arm) is small by 0 When；By ranking results, submodule capacitor voltage is selected to be worth maximum nux(k+1) (upper bridge arm) a submodule output -1, other sons Module output 0.
4) as bridge arm current iux(upper bridge arm) optimizes output level number n less than 0ux(k+1) (upper bridge arm) is more than or equal to 0 When；By ranking results, submodule capacitor voltage is selected to be worth maximum nux(k+1) (upper bridge arm) a submodule output 1, other submodules Block output 0.
5) as bridge arm current iux(upper bridge arm) optimizes output level number n less than 0ux(k+1) when (upper bridge arm) small 0；It presses Ranking results select submodule capacitor voltage to be worth the smallest nux(k+1) (upper bridge arm) a submodule output -1, other submodules are defeated Out 0.

Claims (6)

1. a kind of tundish electromagnetic induction heating system multi layer control method, which is characterized in that including top layer control section, centre Layer control section and bottom control part；The top layer control section includes that control is balanced between whole machine balancing control section, bridge arm Part and alternate balance control section；
The whole machine balancing control section includes: acquisition six all submodule capacitor voltages of bridge arm of electromagnetic induction heating system udxi, and sum and obtain the total capacitance voltage of six bridge armsThe total capacitance voltage addition of six bridge arms is averaged to obtain again Global voltage average value udav, global voltage average value udavWith instruction valueIt controls to obtain three-phase alternating current input electricity through PI after making difference The d axis control instruction of streamThe q axis control instruction of three-phase alternating current input currentIt is set as zero, d axis and q axis control instruction warp Dq/abc converts to obtain three-phase alternating current instructionMaintain all submodule balances of voltage of electromagnetic induction heating system；Wherein, X=a, b, c；
It includes: that each phase upper and lower bridge arm total capacitance voltage is obtained three-phase bridge arm voltage difference as difference that control section is balanced between the bridge arm Δuda,ΔudbWith Δ udc, Δ udbWith Δ udcThe sum of again with 2* Δ udaIt is poor to make, and the d of negative phase-sequence circulation instruction is obtained after PI is controlled Axis control instruction；ΔudcWith Δ udbIt is poor to make, and the q axis control instruction of negative phase-sequence circulation instruction, d axis and q axis control are obtained after PI is controlled System instruction converts to obtain the instruction of three-phase negative/positive loop current through dq/abcWithMaintain the capacitor of three-phase upper and lower bridge arm The balance of voltage；
The alternate balance control section includes: that each phase upper and lower bridge arm total capacitance voltage is summed respectively, obtains three-phase bridge arm electricity Pressure and ∑ udai,∑udbiWith ∑ udci, ∑ udbWith ∑ udcThe sum of with 2* ∑ udaIt is poor to make, and the instruction of positive sequence circulation is obtained after PI is controlled D axis control instruction；∑udbWith ∑ udcIt is poor to make, and the q axis control instruction of positive sequence circulation instruction, d axis and q are obtained after PI is controlled Axis control instruction converts to obtain the instruction of three-phase positive sequence loop current through dq/abcWithMaintain the capacitor of three-phase bridge arm The balance of voltage；
The middle layer control section includes: to establish following objective optimization function: Wherein c1And c2Respectively indicate the weight factor of differential mode voltage and common-mode voltage control target；For differential mode voltage reference Value, is instructed by circulationIt is calculated according to prediction algorithm,For common-mode voltage reference value, instructed by exchange input It is calculated according to prediction algorithm；usxIt (k+1) is differential mode voltage；ucxIt (k+1) is common-mode voltage；Selection makes objective optimization function Being worth the smallest level combinations is optimal output level, obtains the optimization output level number of bridge arm and lower bridge arm next control period nux(k+1) and nlx(k+1)；
The bottom control part includes: the upper bridge arm obtained according to middle layer predictive current control and lower bridge arm next control week The optimization output level number of phase, switch motion is distributed to the submodule of each bridge arm and submodule capacitor voltage is maintained to balance.
2. tundish electromagnetic induction heating system multi layer control method according to claim 1, which is characterized in that three intersections Flow the d axis control instruction of input currentWherein kpScale parameter, k are controlled for PIi Respectively PI controls time of integration parameter.
3. tundish electromagnetic induction heating system multi layer control method according to claim 1, which is characterized in that three intersections Galvanic electricity stream instructs expression formula are as follows:
ωgFor synchronized angular frequency.
4. tundish electromagnetic induction heating system multi layer control method according to claim 1, feature exist In the instruction of three-phase negative/positive loop currentWithExpression formula are as follows:Wherein, ωgFor synchronized angular frequency.
5. tundish electromagnetic induction heating system multi layer control method according to claim 1, which is characterized in that three-phase is just The instruction of sequence loop currentWithExpression formula are as follows:
Wherein,
θ=ω0T, ω0Angular frequency is given for induced current.
6. tundish electromagnetic induction heating system multi layer control method according to claim 1, which is characterized in that the bottom Layer control section specific implementation process include:
Each bridge arm submodule capacitor voltage is acquired, and bridge arm submodule capacitor voltage is ranked up as ascending；
As upper bridge arm current iuxMore than or equal to 0, optimization exports upper bridge arm level number nux(k+1) when being more than or equal to 0, according to sequence As a result, selecting the upper the smallest n of bridge arm Neutron module capacitance voltage valueux(k+1) a submodule exports 1 level, other submodules are defeated 0 level out；Work as iuxMore than or equal to 0, and optimize output level number nux(k+1) less than 0 when, according to ranking results, bridge in selection The maximum n of arm Neutron module capacitance voltage valueux(k+1) a submodule output -1, other submodules export 0 level；
Instantly bridge arm current ilxMore than or equal to 0, optimization output lower bridge arm level number nlx(k+1) when being more than or equal to 0, according to sequence As a result, the selection the smallest n of lower bridge arm Neutron module capacitance voltage valuelx(k+1) a submodule exports 1 level, other submodules are defeated 0 level out；Work as ilxMore than or equal to 0, and optimize output level number nlx(k+1) less than 0 when, according to ranking results, lower bridge is selected The maximum n of arm Neutron module capacitance voltage valuelx(k+1) a submodule output -1, other submodules export 0 level；
As upper bridge arm current iuxLess than 0, optimization exports upper bridge arm level number nux(k+1) when being more than or equal to 0, according to ranking results, The maximum n of bridge arm Neutron module capacitance voltage value in selectionux(k+1) a submodule output 1, other submodules export 0 level；When iuxLess than 0, and optimize output level number nux(k+1) less than 0 when, according to ranking results, bridge arm Neutron module capacitor is electric in selection Pressure is worth the smallest nux(k+1) a submodule output -1, other submodules export 0 level；
Instantly bridge arm current ilxLess than 0, optimization output lower bridge arm level number nlx(k+1) when being more than or equal to 0, according to ranking results, Select the maximum n of lower bridge arm Neutron module capacitance voltage valuelx(k+1) a submodule output 1, other submodules export 0 level；When ilxLess than 0, and optimize output level number nlx(k+1) less than 0 when, according to ranking results, lower bridge arm Neutron module capacitor electricity is selected Pressure is worth the smallest nlx(k+1) a submodule output -1, other submodules export 0 level；
When submodule output 1, left side bridge arm upper tube is open-minded, and down tube is closed, and the right bridge arm upper tube is closed, and down tube is open-minded；Group When module output -1, left side bridge arm upper tube is closed, and down tube is open-minded, and the right bridge arm upper tube is open-minded, and down tube is closed；When submodule exports When 0, left side bridge arm upper tube is closed, and down tube is open-minded, and the right bridge arm upper tube is closed, and down tube is open-minded or left side bridge arm upper tube is open-minded, Down tube is closed, and the right bridge arm upper tube is open-minded, and down tube is closed.
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